Fix the broken triangle generation

[isovector]

This fixes the broken triangles. Detailing was attempting to do... something... and it didn't work.

All of the changed golden tests pass my eyeball test.

Fixes #353

[isovector]

When trying to reproduce #280, I stumbled across this:

writeSTL 3 "/tmp/yo.stl"  $ implicit (\(V3 x y z) -> x^4 + y^4 + z^4
 - 15000) (pure (-20),pure 20) <> (translate (pure 20) $ cubeR 0 True (pure 15)) 

which before this patch looks like this:

and now looks like: